I remember reading somewhere (??? Dr. Jason Fung, perhaps?) that losing just one gram of fat from the pancreas can unclog it so the function of insulin producing beta cells is restored, that they aren't burned out or dead, just clogged up with too much fat. So any type of diet which will cause the loss of enough body fat overall to prompt that relatively small loss from the pancreas would likely do the job to restore insulin sensitivity, I assume so long as the pancreas doesn't get re-clogged by regaining fat. So then the question is more of what type of diet is best for body fat loss, least unpleasant hunger-wise, most sustainable long term, etc. For me that's definitely low carb with usually some degree of IF each day. Unlike a few hundred calories of borderline starvation temporary diet, I can sustain what I do indefinitely.